Hollandus tells to do this with FeSO4 that got rid of it's chrystal water, a stopper and at lower heat over days. That way interesting colors can be seen: Green, white, yellow and red.

Unfortunately, what he describes after that does not happen if you attempt to do it with actual iron vitriol, at least by itself or with common vinegar. Weidenfeld explains that the "trick" here is that the metallic vitriols are dissolved in the secret solvent (the "vinegar" in question) and then they can yield the results described by such writers. The author of the "Triumphal Chariot of Vitriol" says the same thing.

Unfortunately, what he describes after that does not happen if you attempt to do it with actual iron vitriol, at least by itself or with common vinegar. Weidenfeld explains that the "trick" here is that the metallic vitriols are dissolved in the secret solvent (the "vinegar" in question) and then they can yield the results described by such writers. The author of the "Triumphal Chariot of Vitriol" says the same thing.

Another thing: as Weidenfeld points out, it is also quite impossible to carry out this "calcination" of iron vitriol in a sealed flask (indeed, as the decomposition of this salt would give off gases that would eventually burst the glass flask; just look at your video and try to do that in a sealed glass container! I wonder how many poor unsuspecting saps who tried to follow Hollandus' malicious mutilated misleading "recipe" had the sealed heated flasks explode in their faces?), and even if you could pull it off, it would still be useless since the only thing that vitriols purified/crystallized by common water ever give is just the common spirit/oil of vitriol (i.e. sulfuric acid.) Once again, pretty much the same thing is pointed out by the anonymous author of "The Triumphal Chariot of Vitriol". The previous treatment of metallic vitriols by means of the secret solvent is clearly stated as being the key for this type of alchemical processes.